802.11b signal strength variations

While I'm using my 802.11b connection I get a noise level of -95dBm
consistently reported, but the actual signal level tends to be around
-80dBm and almost unusable, or around -40dBm and great.

Oddly, it's never anywhere in between - it flips between good or
terrible, sometimes every few minutes it seems. Does anyone have a
clue what's going on? Does 802.11b have some substandard algorithm for
adjusting transmit power or something? I don't seem to have to do
anything with the laptop or with the access point to have the signal
strength flip between good or lousy - it doesn't seem to rely on the
physical placement of it or anything.

My wife's laptop, a different brand with a different WiFi card, seems
to see the same behavior, and we both seem to have a good connection
at the same time as each other. The access point is a Gigafast
WF711-AP.

I'll try my laptop at work to see if I see the same behavior.

-- Mark

Mark Carroll wrote:
>
> While I'm using my 802.11b connection I get a noise level of -95dBm
> consistently reported, but the actual signal level tends to be around
> -80dBm and almost unusable, or around -40dBm and great.
>
> Oddly, it's never anywhere in between - it flips between good or
> terrible, sometimes every few minutes it seems. Does anyone have a
> clue what's going on?

nope, I have several waps and several wifi clients and they all do
the same thing, even if I'm in the house alone and don't move.

Multipath is what I initially suspected here, since reflecting objects
(metal belt buckle) only have to change position by lambda/4 (2cm or so)
for the received signal to change strength.

Why it happens when nothing is moving though it beyond me.

> Does 802.11b have some substandard algorithm for
> adjusting transmit power or something?

no, constant power.
These aren't very smart devices. This is not a cell phone.

Joe

--
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!

don't laugh but do you have a large fish tank or an indoor pool large
amounts of water will cause signal loss
"Mark Carroll" <(E-Mail Removed)> wrote in message
news:a8h*L38+(E-Mail Removed)...
> While I'm using my 802.11b connection I get a noise level of -95dBm
> consistently reported, but the actual signal level tends to be around
> -80dBm and almost unusable, or around -40dBm and great.
>
> Oddly, it's never anywhere in between - it flips between good or
> terrible, sometimes every few minutes it seems. Does anyone have a
> clue what's going on? Does 802.11b have some substandard algorithm for
> adjusting transmit power or something? I don't seem to have to do
> anything with the laptop or with the access point to have the signal
> strength flip between good or lousy - it doesn't seem to rely on the
> physical placement of it or anything.
>
> My wife's laptop, a different brand with a different WiFi card, seems
> to see the same behavior, and we both seem to have a good connection
> at the same time as each other. The access point is a Gigafast
> WF711-AP.
>
> I'll try my laptop at work to see if I see the same behavior.
>
> -- Mark

"Mark Carroll" <(E-Mail Removed)> wrote in message
news:a8h*L38+(E-Mail Removed)...
> While I'm using my 802.11b connection I get a noise level of -95dBm
> consistently reported, but the actual signal level tends to be around
> -80dBm and almost unusable, or around -40dBm and great.
>
> Oddly, it's never anywhere in between - it flips between good or
> terrible, sometimes every few minutes it seems. Does anyone have a
> clue what's going on? Does 802.11b have some substandard algorithm for
> adjusting transmit power or something? I don't seem to have to do
> anything with the laptop or with the access point to have the signal
> strength flip between good or lousy - it doesn't seem to rely on the
> physical placement of it or anything.
>
> My wife's laptop, a different brand with a different WiFi card, seems
> to see the same behavior, and we both seem to have a good connection
> at the same time as each other. The access point is a Gigafast
> WF711-AP.
>
> I'll try my laptop at work to see if I see the same behavior.
>
> -- Mark

I had the same phenomenon at home. Turned out to be a wireless videolink at
933 Mhz (!). As soon as I switch it off, the signal quality is constant.
Looks like some cheap wireless devices like phones and abovementioned
videolink scream out at all possible harmonics.

BigJim wrote:
> don't laugh but do you have a large fish tank or an indoor pool large
> amounts of water will cause signal loss

How does that work?

--
John Miller
My email address: domain, n4vu.com; username, jsm

A failure will not appear until a unit has passed final inspection.

In article <8UNHb.676953$HS4.4809596@attbi_s01>,
BigJim <(E-Mail Removed)> wrote:
>don't laugh but do you have a large fish tank or an indoor pool large
>amounts of water will cause signal loss
(snip)

No, short of a bit of water, no more than a half gallon, keeping the
Christmas tree watered.

-- Mark

Mark Carroll wrote:

> In article <8UNHb.676953$HS4.4809596@attbi_s01>,
> BigJim <(E-Mail Removed)> wrote:
>>don't laugh but do you have a large fish tank or an indoor pool large
>>amounts of water will cause signal loss
> (snip)
>
> No, short of a bit of water, no more than a half gallon, keeping the
> Christmas tree watered.

Trees also block the signal. ;-)

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

John Miller wrote:

> BigJim wrote:
>> don't laugh but do you have a large fish tank or an indoor pool large
>> amounts of water will cause signal loss
>
> How does that work?
>

Exactly the same way as in a microwave oven. The radio energy gets the
water all excited (those water molecules really need a life :-), which
converts the signal to heat. Any RF that's absorbed in that manner is no
longer available to be received by the computer. Incidentally, the 802.11b
& g wireless gear shares the same spectrum as microwave ovens.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

James Knott wrote:
> Exactly the same way as in a microwave oven. The radio energy gets the
> water all excited (those water molecules really need a life :-), which
> converts the signal to heat. Any RF that's absorbed in that manner is no
> longer available to be received by the computer. Incidentally, the
> 802.11b & g wireless gear shares the same spectrum as microwave ovens.

Sounds like a miracle that you can use WiFi at the beach at all!

While what you say is correct, it's a bit misleading. Just because the
water molecules will absorb RF that's directed at them (they will) doesn't
mean they will "suck" RF that's being radiated in the other 330 degrees
(pick a number) of an omnidirectional signal.

Proximity is another key part of the equation, of course. Having an
aquarium in the house needn't be a factor at all as long as the antennas
are kept away from it.

--
John Miller, N4VU
My email address: domain, n4vu.com; username, jsm

"A verbal contract isn't worth the paper it's printed on."
-Samuel Goldwyn

In article <bspriu$rdq$(E-Mail Removed)>, John Miller <(E-Mail Removed)> wrote:
:Sounds like a miracle that you can use WiFi at the beach at all!

:While what you say is correct, it's a bit misleading. Just because the
:water molecules will absorb RF that's directed at them (they will) doesn't
:mean they will "suck" RF that's being radiated in the other 330 degrees
pick a number) of an omnidirectional signal.

When I read your posting, I was curious about the effect of
an aquarium being within the Fresnel Zone. So I did a bit of
reading at http://www.zytrax.com/tech/wireless/fresnel.htm
which helped but didn't really clear it up for me:

- if a signal is being absorbed by water, then it isn't going
to be deflected and so is not going to arrive at the target
out of phase, and so should not provide a phase problem?

- the referenced page says that zone 1 is "good'ish", adding to
the received power. But then wouldn't deflecting obstacles in zone 1
be desirable?

- the referenced page says that the rule of thumb is that 60% of
zone 1 must be kept clear, and then it says that objects should
be at least 60% of the zone 1 radius away from the line of sight.
But if one had a smaller obstacle close to the line of sight,
could that not count as keeping 60% of the first zone clear,
and yet the obstacle would be closer than 60% of the zone 1 radius?

- the calculator didn't work for me (maybe if I'd been using IE...), so
I looked at the equations they provided, and plugged in some arbitrary
figures. For a 15 metre (~45 feet) interior link with an obstacle at 2
metre (~6 feet), the equations appeared to give an result that the
first fresnel zone would be 465 metres radius. Perhaps someone could
cross-check that result? That'd be about 5 blocks East/West of here,
would trivially cover the busy road a few tens of meters away, and to
the south would cover an important industrial road. I can barely
hold a signal at my sidewalk (~ 10 metres in front), but that might be
affected by trucks rolling by nearly half a kilometer away??
--
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